838 STATE BOARD OF AGRICULTURE. 



performing experiments, for instance, by the freezing point method to 

 determine the effect of application of soluble choniical compounds upon 

 the concentration of the soil solution, it was found that, with few ex- 

 ceptions, the magnitude of the concentration or depression produced, im- 

 mediately after the salt solution was added to the soil and at the end of 

 24 hours, was practically the same. 



In studying the absorption of the base of different salts by the soil, 

 various investigators have noticed that the reaction is very rapid. 

 Especially interesting in this connection is the work of Gedroiz'^ upon 

 the speed of exchange reaction in soils. Gedroiz found that the Ca 

 could be replaced from the soil by NH^ and Na of the NH^Cl and NaCl 

 salt solutions almost immediately. 



From all these evidences, then, it might be accepted as an established 

 fact that the reaction between the soil and Ca(0H)2 is completed very 

 rapidly if not almost instantaneously, and that practically no error 

 enters in the results from this source. 



Besides its simplicity and exceeding rapidity, the freezing point meth- 

 od appears to be also quite accurate, at least from the practical stand- 

 point, in determining the lime requirement of soils. The accuracy seems 

 to vary directly with the lime requirement. If the soil requires about 10,000 

 pounds CaO per 2,000,000 pounds of soil there is probably an error of 

 about 1,000 pounds CaO. If on the other hand, the soil requires only 

 about 1,000 pounds of CaO per acre the error is probably about 200 or 

 300 pounds. The reason that the total error is greater when the lime 

 requirement is high is that the volume of water present is large and the 

 depression caused by 1 c. c. of N/25 Ca(0H)2 for instance, is small as 

 compared to that when the volume of water is less. Since the ther- 

 mometer cannot be depended upon to read accurately, closer than .002° 

 C. it is easier to make a greater total error, although, a smaller percentage 

 of error, in the greater lime requirement than in the small. 



If a larger amount of soil were used doubtless the percentage of error 

 in both cases would be greatly decreased. By using only 2 grams of 

 soil an error of only 1 c. c. of N/25 Ca(0H)2 is equivalent to 1,121.8 

 pounds of CaO' in 2,000,000 pounds of soil. The reason that a larger 

 amount of soil is not used is that the concentration of the Ca(0H)2 

 solution cannot be increased in water above twenty-fifth normality. 

 Consequently, it is necessary to add a large amount of the solution of 

 this strength to the soils possessing a high lime requirement, and the 

 soil tube being of small volume cannot hold all the mass if larger amounts 

 of soil were used. Of course a tube of larger volume could be employed 

 but this may not be advisable. 



Mention has already been made that it is advisable to use in the first 

 determinations large amounts of Ca(0H)2 in order to obtain the limits 

 more quickly, and if necessary to employ smaller quantities in a second 

 set of determinations to obtain the exact amount of Ca(0H)2 required. 

 It should also be stated, however, that it is not advisable to add less 

 than 1 c. c. of Ca(0H)2 in the case of soils which require a large amount 

 of lime; in the case of soils, however, which take up about 1,000 pounds 

 CaO to the acre, less than 1 c. c. might be added each time. The reason 

 for not adding less than 1 c. c. to the soils which possess a high lime 

 requirement becomes evident from what has already been said. In the 



(7) Russ. J. f. Expt. Landw. Vol. 15. No. 3, 1914. 



